As a continuation of previous projects on clinical, pathological, and epidemiologic surveillance of Guamanian amyotrophic lateral sclerosis (ALS) and Parkinsonism-dementia (PD) in the Mariana Islands, a total of 112 cases, including suspects registered as of January 1, 1983, are to be followed at intervals of six months for detailed clnical descriptions of patterns of progression by a qualified neurologist until all of the patients expire. It has been learned that the average duration of ALS is 4.0 to 4.5 years after onset with a range of 2.0 to 25 years. The study of those long surviving cases (over ten years) has been completed. Clinically they showed three patterns: (1) onset with slowly but steady progression at the same pace throughout the course; (2) rapid progression to complete paralysis of the limbs within 1.5 to 3 years and then remaining practically stable for the next 5 to 10 years; (3) onset with minimal atrophy and weakness for the first 5 to 6 years and then rapid step-wise progression to death. A study of the neuropathology of these long-surviving cases by a guest neuropathologist from Japan showed a burnt-out picture: few active areas of neuronal, axonal, or myelin destruction with the remaining neurons appearing surprisingly healthy. A significant number of PD cases were found to show not only lower motor neuron involvement but also severe pelvicrural flexion contractures in the advanced stage of the disease. This observation presents an important question of: (1) motor neuron involvement as a part of the natural history of chronic diseases of the CNS, or (2) a process identical to ALS which occurs in the same patient. If the latter is true, these cases may represent a continuum of ALS and PD, and thus indicate a single etiology of these two diseases.